Efficient heterogeneous electro -Fenton incineration of a contaminant of emergent concern-cotinine- in aqueous medium using the magnetic double perovskite oxide Sr2FeCuO6 as a highly stable catalayst: Degradation kinetics and oxidation products

Abstract

Cotinine, the majormetabolite of nicotine, has been recently detected in the environment and considered as emerging contaminant in waters. Its chemical treatment has scarcely been investigated in the literature. Here, we show for the first time that double perovskite oxide can be used as heterogeneous catalyst for electrochemical advanced oxidation application and cotinine was selected as the target pollutant. Highly stable magnetic double perovskite Sr2FeCuO6 was synthetized for this purpose. The cotinine mineralization in a synthetic sulfate solution of pH 3.0 has been comparatively assessed by anodic oxidation with (AO-H2O2-BDD) and without electro-generated hydrogen peroxide (AO-BDD) and by the heterogeneous electro-Fenton (EF) processes using the magnetic double perovskite Sr2FeCuO6 as the heterogeneous catalyst. The comparative electrolysis experiments were carried out with 500 mL stirred reactor equipped with a boron-doped diamond (BDD) and a carbon felt cathode. Faster mineralization decay was observed with the electro Fenton process due to the additional oxidation by hydroxyl radicals produced from Fenton´s reaction between the iron sites and the electro-generated hydrogen peroxide at the cathode. Moreover, the synergistic effect of the cuprous sites was pointed out. The leaching test confirms the high stability of the catalyst and its heterogeneous action. The influence of current intensity and cotinine concentration was examined. Seven stable organics intermediates were detected and four of them were identified as N-Hydroxymethyl norcotinine, norcotinine, 4-oxo-4-(3-pyridyl) butanoic acid and 4-(3-Pyridyl)-3-butenoic Acid. The initial N was released as nitrate and, in smaller proportion, as ammonium ion. Short chain aliphatic acids, mainly oxalic and formic acids were detected. EPR analyses revealed that cotinine was mainly decomposed by the attack of OH. A reaction sequence for cotinine mineralization involving all the detected products is finally proposed. The reusability of the magnetic catalyst for at least 3 times highlights the practical applicability of the envisaged heterogeneous process.